The Saudi-led coalition battling Shiite Houthi rebels in Yemen closed the country’s air, sea and land borders Monday and accused Iran of being behind a weekend missile attack on Riyadh, saying it “may amount to an act of war”.

The missile was the first aimed by the Shiite rebels at the heart of the Saudi capital, underscoring the growing threat posed by the raging conflict.

“The leadership of the coalition forces therefore considers this … a blatant military aggression by the Iranian regime which may amount to an act of war,” the official Saudi news agency SPA said in a statement.

Smouldering debris landed inside the King Khalid International Airport, just north of Riyadh, after the missile was shot down but authorities reported no major damage or loss of life.

Watch: Saudi military fires missile defences in Saturday’s attack

Yemen’s complex war pits the Saudi-backed government of President Abedrabbo Mansour Hadi against former president Ali Abdullah Saleh and his Iran-backed Houthi rebel allies.

The Saudi statement said that the borders were being closed “to fill the gaps in the inspection procedures which enable the continued smuggling of missiles and military equipment to the Houthi militias loyal to Iran in Yemen”.

Despite the temporary closure of the air, sea and land ports, Saudi would protect “the entry and exit of relief and humanitarian personnel”.

“The coalition … affirms the kingdom’s right to respond to Iran at the appropriate time and in the appropriate form,” it added.